Fluorinated greases having a low torque at low temperatures

ABSTRACT

Fluorinated greases comprising: (A) from 1% to 50% by weight of a thickener; (B) from 99% to 50% by weight of a mixture of: (B1) from 0, 1 to 100% by weight of a compound of structure: 
 
X 1 —O(CF 2 O)n(CF 2 CF 2 O) m (CF 2 CF 2 CF 2 O) p (CF 2 CF 2 CF 2 CF 2 O) q —X 2   (I) 
wherein: 
             X 1 , X 2  have formula —(CF 2 ) Z CF 3  wherein z is an integer between 0 and 3; n is an integer between 1 and 200; m is an integer between 0 and 200; p, q are integers between 0 and 10; with the proviso that: the (p+q)/(p+q+m+n)≦0.05; m/n≦0.7; the number average molecular weight of (I) is between 1,000 and 10,000; the kinematic viscosity at 40° C. is lower than 20 cSt; and        (B2) from 99.9% to 0% by weight of a perfluoropolyether oil having a kinematic viscosity at 40° C. higher than 15 cSt and comprising repeating units of the type (CFXO) wherein X is F or CF 3 ; —CF 2 CF 2 O—, —C 3 F 6 O, —CF(CF 3 ) CF 2 O, —CF 2 CF (CF 3 ) O—, statistically distributed along the chain.

The present invention relates to fluorinated greases having a low torque.

The invention specifically relates to perfluoropolyether-based greases having lower torques at low temperatures, in particular at temperatures lower than −40° C.

The invention more specifically relates to perfluoropolyether grease compositions having improved torques at −40° C., in particular at temperatures lower than −40° C., and to the use of said compositions in the lubrication in a wide temperature range, preferably between −100° C. and +180° C.

It is known in the prior art to use perfluoro-polyether oils as lubricants in a wide temperature range, in particular at very low temperatures, for example in the aerospace and refrigeration industry. Among these lubricants, those used for the low temperatures have a typically linear structure, as for example FOMBLIN® marketed by Solvay Solexis S.p.A. These oils are used alone or formulated with particular thickeners, for example polytetrafluoroethylene (PTFE), to obtain greases.

In case of greases to be used at low temperatures, the lowering of the torques is essential to reduce the energy for the handling of mechanical parts, for example bearings, in contact with the grease. In particular in aerospace applications fluorinated greases having lubricating properties at −40° C., and even at much lower temperatures −40° C., are required.

Fluorinated greases having a low torque at −40° C., are known. For example, U.S. Pat. No. 6,329,326 describes greases for ball-bearings for cars containing linear perfluoropolyether oils having a kinematic viscosity, measured at 40° C., between 40 and 160 cSt, and PTFE having an average diameter lower than 0.1 micron. These greases are characterized by a low torque at −40° C., and a good durability at 180° C. and can therefore be used in a temperature range from −40° C., to 200° C. In this patent, applications at temperatures lower than −40° C., are not mentioned, the behaviour of the greases at temperatures lower than −40° C., is described neither.

U.S. Pat. No. 6,723,684 describes greases for bearings in the automotive field and planes, having the following composition: a perfluoro-polyether oil having a linear structure and viscosity, at 40° C., equal to or lower than 25 cSt; a perfluoro-polyether oil having a linear structure and viscosity, at 40° C., equal to or higher than 250 cSt; PTFE as thickener. The two oils used to prepare the grease are mixed so as to have a total viscosity, measured at 40° C., from 40 to 150 cSt. These greases are used in a temperature range from −40° C., to +180° C. Torques at −40° C., are given, however values and/or applications at temperatures lower than −40° C., are not reported.

The need was therefore felt to have available fluorinated greases having low torques at temperatures lower than or equal to −40° C., in particular values lower than those of the greases based on linear perfluoropolyether oils of the prior art.

The Applicant has surprisingly and unexpectedly found fluorinated greases comprising particular linear perlfuoropolyethers usable in applications at temperatures lower than −40° C., showing torques lower than those of the prior art greases.

It is therefore an object of the present invention fluorinated greases comprising from (% by weight):

-   (A) 1% to 50%, preferably from 10% to 40%, of one or more     thickeners; -   (B) 99% to 50%, preferably between 90% and 60%, of a mixture of the     following perfluoropolyethers:     -   (B1) 0.1% to 100%, preferably from 5% to 100%, of a         perfluoropolyether having the following formula:         X₁—O(CF₂)_(n)(CF₂CF₂O)_(m)(CF₂CF₂CF₂)_(p)(CF₂CF₂CF₂CF₂O)_(q)X₂  (I)         -   wherein:             -   the repeating units —CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O—,                 —CF₂CF₂CF₂CF₂O— are statistically distributed along the                 backbone;             -   —X₁ and —X₂ are perfluoroalkyl chain end groups equal to                 or different from each other, having formula                 —(CF₂)_(z)CF₃ wherein z is an integer from 0 to 3;             -   n is an integer between 1 and 200,             -   m is an integer between 0 and 200,             -   p, q are integers between 0 and 10, preferably between 0                 and 5, more preferably between 0 and 1;         -   with the proviso that:             -   the ratio (p+q)/(p+q+m+n) is lower than or equal to                 0.05, or also equal to 0;             -   the ratio m/n, (when n is different from 0), is lower                 than or equal to 0.7, preferably lower than 0.5, more                 preferably lower than 0.35;             -   the number average molecular weight of the compounds of                 formula (I) is between 1,000 and 10,000, preferably                 between 2,000 and 8,000, more preferably between 2,400                 and 5,000;             -   the kinematic viscosity, at 40° C., is lower than 20                 cSt; and             -   the chlorine atoms, determined by ¹⁹F NMR, are                 substantially absent.     -   (B2) 99.9% to 0%, preferably from 95% to 0%, of a         perfluoropolyether oil having a kinematic viscosity, at 40° C.,         higher than 15 cSt and comprising repeating units of the type         (CFXO) wherein X is F or CF₃;         -   —CF₂CF₂O—, —CF(CF₃)CF₂O—, —(F₂CF(CF₃)O—, statistically             distributed along the backbone;             and optionally -   (C) 0% to 10% with respect to the total weight of (A)+(B),     preferably from 1% to 3%, of one or more additives selected from     anti-wear additives for high or low loads, anti-rust, antioxidant     additives, stabilizers.

The thickener (A) can be selected from the known thickeners of the prior art, for example talc, silica, polytetrafluoroethylene (PTFE), or their mixtures. When silica is used as thickener, the amounts range from 1 to 10% by weight with respect to the total weight of (A)+(B); when talc or PTFE are used, the amounts range from 5% to 40% by weight, more preferably from 5% to 35%, with respect to the total (A)+(B).

Preferably, as thickener, PTFE is used, more preferably PTFE having an average particle size between 0.01 μm and 0.3 μm. PTFE, used as thickener, can be obtained by the known polymerization techniques, in particular by microemulsion, emulsion or dispersion polymerization. Furthermore the PTFE can also be subjected to irradiation. Known processes for preparing PTFE are described in patents EP 1,520,906, U.S. Pat. No. 4,864,006, U.S. Pat. No. 6,297,334, U.S. Pat. No. 6,576,703.

Compounds (B1) of formula (I), wherein the chlorine atoms, determined by ¹⁹F NMR, are substantially absent, are compounds wherein the chlorine atoms are lower than the sensititivy limit of the analytical ¹⁹F NMR method.

Component (B1) is liquid at 20° C., shows a low vapour pressure, a high viscosity index and therefore it can be considered a lubricating oil. Besides it shows pour point values preferably lower than −90° C.

Component (B2) can be selected from the following classes:

(1) E-O—(CF₂CF(CF₃)O)_(m′)(CFXO)_(n′)-E′

-   -   wherein:     -   X is equal to F or CF₃;     -   E and E′, equal to or different from each other, are selected         from CF₃, C₂F₅ or C₃F₇, one fluorine atom of one or both the end         groups being replaceable with Cl and/or H;     -   m′ and n′ are integers such that the ratio m′/n′ is between 20         and 1,000, n′ being different from zero; the units being         statistically distributed along the backbone, the viscosity of         the product being as above.

These polymers can be obtained by perfluoropropene photo-oxidation as described in GB 1,104,432, and by subsequent conversion of the end groups as described in GB 1,226,566;

(2) C₃F₇O(CF(CF₃)CF₂O)_(o′)-D

-   -   wherein:     -   D is equal to —C₂F₅ or —C₃F₇, one fluorine atom of one or both         the end groups being replaceable with Cl and/or H;     -   o′ is an integer such that the viscosity of the product is as         above.

These polymers can be prepared by ionic oligomerization of the perfluoropropylenoxide and subsequent treatment with fluorine as described in U.S. Pat. No. 3,242,218;

(3) {C₃F₇O—(CF(CF₃)CF₂O)_(p)—CF(CF₃)—}₂

-   -   wherein:     -   p′ is an integer such that the viscosity of the product is as         above, one F atom of one or both the end groups C₃F₇ being         replaceable with Cl and/or H.

These products can be prepared by ionic telomerization of

-   -   the perfluoropropylenoxide and subsequent photochemical         dimerization as reported in U.S. Pat. No. 3,214,478;

(4) E-O—(CF₂CF(CF₃)O)_(q′)(C₂F₄O)_(r′)(CFX)_(s′)E′

-   -   wherein:     -   X is equal to F or CF₃;     -   E and E′, equal to or different from each other, are as above;     -   q′, r′ and s′ are integers including 0, and such that the         viscosity of the product is as above.

These polymers are obtainable by photooxidation of a mixture of C₃F₆ and C₂F₄ and subsequent treatment with fluorine as described in U.S. Pat. No. 3,665,041;

(5) E-O-(c₂F₄O)_(t′)(CF₂O)_(u′)E′

-   -   wherein:     -   E and E′, equal to or different from each other, are as above;     -   t′ and u′ are integers such that the ratio t′/u′ is between 0.1         and 5, u′ being different from 0, and the viscosity of the         product is as above.     -   These polymers are obtained by photooxidation of C₂F₄ as         reported in U.S. Pat. No. 3,715,378 and subsequent treatment         with fluorine as described in U.S. Pat. No. 3,665,041;         (6) E-O—(CF₂CF₂CF₂O)_(v′)-E′     -   wherein:     -   E and E′ equal to or different from each other, are as above;     -   v′ is a number such that the viscosity of the product is as         above.     -   These polymers are obtained as described in EP 148,482;         (7) D-O—(CF₂CF₂O)_(z′)-D′     -   wherein:     -   D and D′, equal to or different from each other, are selected         from C₂F₅ or C₃F₇, one fluorine atom of one or both the end         groups being replaceable with Cl and/or H;     -   z′ is an integer such that the viscosity of the product is as         above.     -   These polymers can be obtained as reported in U.S. Pat. No.         4,523,039;         (8) E₁-O(CF₂O)_(n)(CF₂CF₂O)_(m)-(CF₂CF₂CF₂O)_(p)         (CF₂CF₂CF₂CF₂O)_(q)-E₂     -   wherein:     -   E₁ and E₂ are perfluoroalkyl end groups, equal to or different         from each other, having formula —(CF₂)_(z)CF₃ wherein z is an         integer from 0 to 3;     -   n, m, p, q are integers equal to or different from each other         between 0 and 100 and selected so that the viscosity of the oil         is as above and such that the ratio m/n is between 2 and 20, n         being different from 0; (p+q)/(n+m−+p+q) is between 0.05 and         0.2, (n+m+p+q) being different from 0; n/(n+m+p+q) is between         0.05 and 0.40, (n+m+p+q) being different from 0.

These polymers can be obtained according to EP 1,454,938.

The classes (1), (4), (5), (8) or their mixtures are preferred, the classes (5) and (8) or their mixtures are more preferred.

The mixture of oils (B1)+(B2) preferably has a kinematic viscosity lower than 40 cSt at 40° C.

Optionally, as said, additives commonly used in the lubrication field, f.i. anti-wear additives for high and low loads, anti-rust, antioxidant additives and/or stabilizers can be present in the lubricating composition of the present invention, in an amount not higher than 10% by weight with respect to the total composition. As stabilizing additives, the perfluoropolyether dinitro derivative compounds, described in patent application US 2003/0203,823; the pyridine derivatives obtained according to patent application US 2004/235,685, can be mentioned. As anti-wear additives, it can be mentioned molybdenum sulphide, molybdenum organic compounds, boron nitride, graphite, phosphazene derivatives, in particular phosphazene derivatives containing perfluoro-polyether chains, for example as those described in patent application US 2003/176.738. As anti-rust additives, the disodic sebacate, sodium carbonate, functionalized derivatives of carboxylic acids containing perfluoropolyether chains, for example as those described in U.S. Pat. No. 5,000,864 or in U.S. Pat. No. 6,025,307, can be mentioned.

Component (B1) can be prepared, for example, according to the following process comprising the following steps:

-   a) synthesis of a peroxidic perfluoropolyether, obtainable by one of     the following reactions:     -   a1) tetrafluoroethylene (TFE) photooxidation, in the presence of         UV light, at a temperature between −40° C. and −100° C., in         solvents liquid under the reaction conditions, of formula:         C_(y)F_((2y+2−x))H_(x)  (II)         -   wherein y is an integer from 2 to 4; x is an integer equal             to 0 or 1;         -   in the presence of elemental fluorine as chain transfer             agent, diluted with an inert gas;     -   or     -   a2) TFE oxidation by using as radical initiator fluorine or         hypofluorites of formula         R_(f)OF  (III)         -   R_(f) being a perfluoroalkyl radical from 1 to 3 carbon             atoms,         -   by operating in the temperature range from −40° C. to             −100° C. at a pressure between 0 and 12 bar, in an inert             solvent;     -   preferably a2) is used; -   b) thermal treatment of the peroxidic product obtained in step a) at     a temperature from 150° C. to 250° C., optionally in the presence of     chain transfer agent selected from elemental fluorine and one or     more hypofluorites of formula (III); -   c) treatment with elemental fluorine of the polymer obtained in b)     at temperatures from 100° C. to 250° C., or by treatment with     fluorine in the presence of UV radiations, by operating at     temperatures between −50° C. and 120° C.     In step a1) the fluorine is generally added in amounts such that the     molar ratio fluorine/tetrafluoroethylene is between 2·10⁻² and     1.2·10⁻³, preferably between 1.2·10⁻² and 1.7·10⁻³ and is diluted     with an inert gas in ratios by volume from 1/50 to 1/1,000.

In step a1) preferably the solvents are the following: perfluoropropane (C₃F₈), hydropentafluoroethane (C₂F₅H) and 2-hydroheptafluoropropane (CF₃CFHCF₃), C₄F₉H (for example CF₃C—FHCF₂CF₃, (CF₃)₃CH, HCF₂CF₂CF₂CF₃).

The solvent used in step a1) is liquid at the synthesis temperatures (−40°÷−80° C.) and solubilizes the peroxidic polymer even in high molecular weights forming a homogeneous solution. This represents a remarkable advantage since there is no separation of the peroxidic polymer. This makes possible the industrial use of said process as no cloggings of the industrial plant piping due to uncontrolled viscosity increase take place. Further the thermal exchanges are extremely effective and this avoids uncontrolled degradation of the peroxidic polymer.

Besides, the solvents used in step a1) allow a high reaction kinetics, so to maintain high productivities combined with a low peroxidic content in the polymer, lower than 4-5 g of active oxygen/100 g of product, to avoid explosion risks.

As said, the fluorine used in step a1) must be diluted with a gas. Generally an inert gas, as nitrogen or helium is used. Oxygen can also be used as diluent. In fact, when undiluted fluorine is used, the fluorine produces uncontrolled local reactions and gaseous decomposition products. The latter cause stopping of the process due to fouling of the reactor and of the optical system (UV lamp) in case of polymerization in the presence of UV radiations. Besides, in these cases, there can be an uncontrolled increase of the peroxidic content P.O., higher than 4-5 g of active oxygen/100 g of product, bringing to explosion risks in the system. When it is used diluted, the fluorine acts in step a1) as chain transfer agent with a very high selectivity, of the order of 90%.

The fluorine furthermore, in step a1), reduces and substantially eliminates the reaction induction times avoiding the use of reaction activators.

In step a2), wherein the TFE oxidation is carried out without using the UV light, the solvents can be those above mentioned, or chlorinated solvents. For example CF₂Cl₂, optionally in admixture with COF₂ can be mentioned.

In step a2) the molar ratio TFE/chemical initiator ranges from 10 to 200, preferably from 40 to 120.

In step b) the use of chain transfer agent can be omitted when the control of the molecular weight is not necessary. This happens, for example, when the viscosity of the peroxidic product is lower than 5,000 cSt.

In step b) generally fluorine or hypofluorites of formula (III), when present, are used with a flow-rate from 1·10⁻² to 3, preferably from 2·10⁻² to 2 moles·h/Kg polymer.

Step a) and step b) of the process of the present invention can be carried out in a discontinous, semicontinuous or continuous way.

Step b) ends when the peroxidic content in the polymer is substantially absent. This means that the P.O. value is equal to or lower than the sensitivity limit of the analytical method used (1 ppm), by titration with thiosulphate of the iodine developed by the reaction of the peroxidic polymer with sodium iodide. Generally the thermal treatment times are from 10 to 30 hours, depending on the P.O. and the temperature used in this step.

Step c) is usually carried out in a discontinuous way. The reaction ends when, at ¹⁹F NMR analysis, the functional end groups (mainly —OCF₂COF and —OCOF) have been transformed into perfluoroalkyl end groups (method sensitivity limit: 1 meq/Kg polymer).

In step c) the fluorine is fed in amounts so to have a concentration in the perfluoropolyether generally corresponding to the fluorine solubility limit. At the temperature used in the step, it is of the order or 10⁻² moles of fluorine/litre of polymer.

Optionally, the product can be distilled to obtain fractions having a given number average molecular weight and a determined distribution of the molecular weights.

The fluorinated greases of the present invention can be obtained according to the mixing procedures described in the prior art, for example comprising the following steps:

-   -   feeding of the oil and/or mixture of lubricating oils (B1),         (B2), in a mixer and degassing under vacuum at 60° C. for 2         hours at 0.1 mbar;     -   gradual addition of component (A) (thickener) until reaching the         desired composition;     -   optional addition of component (C) (additive): when the additive         is liquid it is premixed with the basic oil or the mixture         before adding the thickener; when the additive is solid, it is         premixed with the thickener powder before the gradual addition         to the basic oil or to the mixture;     -   constant stirring for at least 8 hours under vacuum;     -   discharge of the obtained grease and its refining by passage on         tri-roller refiner.

The consistency of the greases of the present invention depends on the total concentration of the thickener used in the composition; in particular by increasing the thickener content, the penentration value decreases. The amounts of thickener (A) reported above allow to obtain all the penetration NLGI classes defined by the ASTM D 217 method, from degree 000, corresponding to a penetration value of 475 mm/10′, to degree 6, corresponding to 85 mm/10′. This allows to satisfy the various requirements in a wide application range.

The lubricating compositions of the present invention show a torque lower than those of the prior art. (see the comparative Examples). Furthermore said compositions can be used even at temperatures lower than −40° C., preferably lower than −60° C., for applications at very low temperatures as for example in the aerospace and refrigeration industry. In applications wherein one operates at temperatures from −40° C. to −80° C., component B) is preferably formed of an oil mixture, wherein the oil (B1) is present up to at most 50% by weight with respect to (B2), preferably up to 30%, and the kinematic viscosity of the mixture is preferably lower than 40 cSt, more preferably lower than 35 cSt. In applications at temperatures lower than −80° C., component (B) is preferably formed of the oil (B1) alone.

It is surprising and unexpected that the invention greases comprising compounds of formula (I) show at −60° C. starting torque values much lower than those of the greases prepared according to the prior art, the penetration and the viscosity of the basic oils being substantially the same (see the comparative Examples).

The lubricating compositions of the present invention show furthermore the advantage to be usable in applications having wide temperature ranges, for example −100/+180° C. It has indeed been found that the compositions wherein the oil (B2) belongs to the class (8) show a high thermal stability at 180° C. combined with a low torque value. Therefore said compositions can be used as lubricants in applications where wide temperature ranges are present.

Some illustrative but not limitative Examples of the present invention follow.

EXAMPLES

Characterization

Determination of the Torque at Low Temperature

The torque measurements have been carried out at different temperatures (−40° C., −60° C. and −70° C.) by using a ball-bearing according to what described in the ASTM D 1478 method. The measured parameters are the “starting torque”, representing the initial starting point of the bearing, and the “running torque”, which represents the working stress after 1 test hour. The measure unit is the g·cm.

Determination of the Kinematic Viscosity

The kinematic viscosity at a given temperature has been determined by using capillary Cannon-Fenske type viscometers according to the ASTM D 445 method.

Determination of the Penetration (or Grease Consistency)

The penetration value has been evaluated according to the ASTM D 217 method. The higher the penetration value and the lower the grease consistency.

Example 1

70 g of a perfluoropolyether oil of structure (I) having number average molecular weight 2,467, m/n 0.33, (p+q)/−(p+q+m+n) 0.016 and kinematic viscosity at 20° C. of 13 cSt, were additioned with 30 g of PTFE, commercially known as Algoflon® L206. A grease having a penetration of 309 mm/10′ was obtained.

The starting torque and running torque values were measured, at the temperature of −70° C., and resulted equal to 578 g·cm and 44 g·cm, respectively.

Example 1A (Comparative)

The Example 1 was repeated but by using as component B) a perfluoropolyether oil of class (5) wherein m/n=1.1, having a kinematic viscosity at 40° C. between 40 cSt and 160 cSt and equal to 151 cSt.

A grease having a penetration of 290 mm/10′ was obtained.

The starting torque and running torque values were measured, at the temperature of −70° C., and resulted equal to 3,667 g·cm and 1,581 g·cm, respectively.

The comparison of the data of the Example 1 with those of the Example 1A (comparative) shows that the invention greases show torque values at −70° C. much lower than those of the greases obtained according to the prior art teachings, the oil/thickener content being equal.

Example 2

70 g of a perfluoropolyether oil of structure (I) wherein m/n=0.31, (p+q)/(p+q+m+n)=0.016 and having number average molecular weight of 3,985 and a kinematic viscosity at 20° C. of 19 cSt, were additioned with 30 g of PTFE, commercially known as Algoflon® L206. A grease having a penetration of 315 mm/10′ was obtained.

The grease starting torque and running torque values were measured at the temperature of −60° C., and resulted equal to 358 g·cm and 34 g·cm, respectively.

Example 3 (Comparative)

The Example 2 was repeated but by replacing the oil of formula (I) with 70 g of a linear perfluoropolyether oil of class (5), wherein m/n 0.8, having a number average molecular weight equal to 4,000, commercially known as Fomblin® Z03.

A grease having a penetration of 312 mm/10′ was obtained.

The starting torque and running torque values of the grease were measured at the temperature of −40° C., and resulted equal to 455 g·cm and 198 g·cm, respectively.

The starting torque and running torque values of the grease were measured also at the temperature of −60° C., and resulted equal to 676 g·cm and 181 g·cm, respectively.

The comparison of the data of the Example 2 with those of the Example 3 (comparative) shows that the greases obtained from the perfluoropolyether oils of structure (I) of the present invention show a torque value at temperatures lower than −40° C. reduced by 50% in comparison with greases obtained by using a commercial oil as basic oil, the grease penetration and substantially the basic oil viscosity being equal. It results furthermore that the greases of the invention show starting torque and running torque values at −60° C. lower than those of the greases obtained from commercial linear perfluoro-polyether oils measured at −40° C.

Furthermore also the comparison of the data of the Example 1 with those of the Example 3 (comparative) shows the same behaviour described above.

Example 4

A mixture B) of oils was prepared formed of:

-   (B1) 76 g of the oil of structure (I) of the Example 1; -   (B2) 24 g of an oil of class (5) having viscosity at 40° C. of 320     cSt.

The kinematic viscosity of the so obtained mixture, measured at 40° C., is lower than 40 cSt and is equal to 23.1 cSt.

30 g of PTFE, commercially known as Algoflon® L206, were added to 70 g of the previously prepared mixture.

A grease having a penetration of 317 mm/10′ was obtained. The starting torque and running torque values of the grease were measured, at the temperatures of −40° C., and −60° C., and the following results were obtained: T (° C.) Starting torque (g · cm) Running torque (g · cm) −40 286 126 −60 338 92

Example 5 (Comparative)

The Example 4 was repeated but by replacing the oil of formula (I) with a perfluoropolyether oil of class (5) having a substantially equal kinematic viscosity and lower than 25 cSt.

The mixture of basic oils B) was prepared so as to obtain a mixture having a kinematic viscosity substnatially equal to that of the Example 4, by mixing:

-   -   96 g of a perfluoropolyether oil of class (5) wherein m/n=0.8         and having kinematic viscosity measured at 40° C. lower than 25         cSt and equal to 17 cSt;     -   4 g of a perfluoropolyether oil of class (5) having kinematic         viscosity at 40° C. higher than 250 cSt and equal to 320 cSt.

The kinematic viscosity of the so obtained mixture, measured at 40° C., is 25.5 cSt.

A grease having a penetration of 311 mm/10′ was then obtained.

The starting torque and running torque values of the grease were measured at the temperatures of −40° C. and −60° C., and the following results were obtained: T Starting torque Running torque (° C.) (g · cm) (g · cm) −40 299 162 −60 819 153

The comparison of the data of the Example 4 with those of the Example 5 (comparative) shows that, the grease penetration and substantially the viscosity of the basic oil mixture (component B) being equal, the greases of the invention, even showing a torque value at −40° C., substantially equal to that of the greases containing linear perfluoropolyether oils according to U.S. Pat. No. 6,723,684, show at −60° C. a twice lower starting torque value. 

1. Fluorinated greases comprising from (% by weight): (A) 1% to 50%, preferably from 10% to 40%, of one or more thickeners; (B) 99% to 50%, preferably from 90% to 60%, of a mixture of the following perfluoropolyethers: (B1) 0.1% to 100%, preferably from 5% to 100%, of a perfluoropolyether having the following formula: X₁—O(CF₂O)_(n)(CF₂CF₂O)_(m)(CF₂CF₂CF₂O)_(p)(CF₂CF₂CF₂CF₂O)_(q)—X₂  (I) wherein: the repeating units —CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O—, —CF₂CF₂CF₂CF₂O— are statistically distributed along the backbone; —X₁ and —X₂ are perfluoroalkyl chain end groups equal to or different from each other, having formula —(CF₂)_(z)CF₃ wherein z is an integer from 0 to 3; n is an integer between 1 and 200, m is an integer between 0 and 200, p, q are integers between 0 and 10, preferably between 0 and 5, more preferably between 0 and 1; with the proviso that: the ratio (p+q)/(p+q+m+n) is lower than or equal to 0.05, or also 0; the ratio m/n, (when n is different from 0), is lower than or equal to 0.7, preferably lower than 0.5, more preferably lower than 0.35; the number average molecular weight of the compound of formula (I) is between 1,000 and 10,000, preferably between 2,000 and 8,000, more preferably between 2,400 and 5,000; the kinematic viscosity, at 40° C., is lower than 20 cSt; and the chlorine atoms, determined by ¹⁹F NMR, are substantially absent; (B2) 99.9% to 0%, preferably from 95% to 0%, of a perfluoropolyether oil having a kinematic viscosity at 40° C. higher than 15 cSt and comprising repeating units of the type (CFXO) wherein X is F or CF₃; —CF₂CF₂O—, —CF (CF₃) CF₂O—, —CF₂CF(CF₃)O—, statistically distributed along the backbone; and optionally (C) 0% to 1.0% with respect to the total weight of (A)+(B), preferably from 1% to 3%, of one or more additives selected from anti-wear additives for high or low loads, anti-rust, antioxidant additives, stabilizers.
 2. Greases according to claim 1, wherein the thickener (A) is selected from the known thickeners of the prior art, for example talc, silica, polytetrafluoroethylene (PTFE), or their mixtures.
 3. Greases according to claim 1, wherein the thickener is silica, in amounts ranging from 1 to 10% by weight with respect to the total weight of (A)+(B).
 4. Greases according to claim 1, wherein the thickener is talc or PTFE, in amounts ranging from 5% to 40% by weight, more preferably from 5% to 35%, with respect to the total (A)+(B).
 5. Greases according to claim 4, wherein the thickener is PTFE, more preferably PTFE having an average particle size between 0.01 μm and 0.3 μm.
 6. Greases according to claim 1, wherein component (B2) is selected from the following classes (1) E-O— (CF₂CF(CF₃)O)_(m′)(CFXO)_(n′)-E′ wherein: X is equal to F or CF₃; E and E′, equal to or different from each other, are selected from CF₃, C₂F₅ or C₃F₇, one fluorine atom of one or both the end groups being replaceable with Cl and/or H; m′ and n′ are integers such that the m′/n′ ratio is between 20 and 1,000, n′ being different from zero; the units being statistically distributed along the backbone, the viscosity of the product being as above; (2) C₃F₇O(CF (CF₃) CF₂O)_(o′)-D wherein: D is equal to —C₂F₅ or —C₃F₇, one fluorine atom of one or both the end groups being replaceable with C1 and/or H; o′ is an integer such that the viscosity of the product is as above; (3) {C₃F₇O—(CF(CF₃) CF₂O)_(p′)—CF(CF₃)—}₂ wherein: p′ is an integer such that the viscosity of the product is as above, one F atom of one or both the end groups C₃F₇ being replaceable with Cl and/or H; (4) E-O— (CF₂CF(CF₃)O)_(q), (C₂F₄O)_(r), (CFX)_(s), -E′ wherein: X is equal to F or CF₃; E and E′, equal to or different from each other, are as above; q′, r′ and s′ are integers including 0, and such that the viscosity of the product is as above; (5) E-O—(C₂F₄O)_(t′)(CF₂O)_(u′)-E′ wherein: E and E′, equal to or different from each other, are as above; t′ and u′ are integers such that the ratio t′/u′ is between 0.1 and 5, u′ being different from 0, and the viscosity of the product is as above; (6) E-O—(CF₂CF₂CF₂O)_(v′)-E′ wherein: E and E′, equal to or different from each other, are as above; v′ is a number such that the viscosity of the product is as above; (7) D-O—(CF₂CF₂O)_(z), -D′ wherein: D and D′, equal to or different from each other, are selected from C₂F₅ or C₃F₇, one fluorine atom of one or both the end groups being replaceable with C1 and/or H; z′ is an integer such that the viscosity of the product is as above; (8) E₁-O(CF₂O)_(n)(CF₂CF₂O)_(m)—(CF₂CF₂CF₂O)_(p)(CF₂CF₂CF₂CF₂O)_(q)-E₂ wherein: E₁ and E₂ are perfluoroalkyl end groups, equal to or different from each other, having formula —(CF₂)_(z)CF₃ wherein z is an integer from 0 to 3; n, m, p, q are integers equal to or different from each other between 0 and 100 and selected so that the viscosity of the oil is as above and such that the ratio m/n is between 2 and 20, n being different from 0; (p+q)/(n+m+p+q) is between 0.05 and 0.2, (n+m+p+q) being different from 0; n/(n+m+p+q) is between 0.05 and 0.40, (n+m+p+q) being different from
 0. 7. Greases according to claim 6, wherein component (B2) is selected from the classes (1), (4), (5), (8) or their mixtures, more preferably from the classes (5) and (8) or their mixtures.
 8. Greases according to claim 1 comprising additives commonly used in the lubrication field, preferably anti-wear additives for high and low loads, anti-rust, antioxidant additives and/or stabilizers, in an amount not higher than 10% by weight with respect to the total composition.
 9. Greases according to claim 8, wherein the stabilizing additives are selected from the perfluoropolyether dinitro derivative compounds and the perfluoropolyether pyridine derivatives.
 10. Greases according to claim 8, wherein the anti-wear additives are selected from molybdenum sulphide, molybdenum organic compounds, boron nitride, graphite, phosphazene derivatives, preferably phosphazene derivatives containing perfluoropolyether chains.
 11. Greases according to claim 8, wherein the anti-rust additives are selected from disodic sebacate, sodium carbonate, functionalized derivatives of carboxylic acids containing perfluoro-polyether chains.
 12. A process for preparing the greases of claim 1, comprising the following steps: feeding of the oil and/or mixture of lubricating oils (B1), (B2), in a mixer and degassing under vacuum at 60° C. for 2 hours at 0.1 mbar; gradual addition of component (A) (thickener) until reaching the desired composition; optional addition of component (C) (additive): when the additive is liquid it is premixed with the basic oil or in the mixture before adding the thickener; when the additive is solid, it is premixed with the thickener powder before the gradual addition to the basic oil or to the mixture; constant stirring for at least 8 hours under vacuum; discharge of the obtained grease and its refining by passage on tri-roller refiner.
 13. Use of the greases of claim 1 for the lubrication at temperatures lower than −40° C., preferably lower than −60° C., for applications in the aerospace and refrigeration industry.
 14. Use according to claim 13 at temperatures from −40° C. to −80° C., wherein component B) is formed of an oil mixture, wherein the oil (B1) is present up to at most 50% by weight with respect to the oil (B2), preferably up to 30%, and the kinematic viscosity of the mixture is preferably lower than 40 cSt, more preferably lower than 35 cSt.
 15. Use according to claim 13 at temperatures lower than −80° C. wherein component (B) of the grease is formed of the oil (B₁).
 16. Use of the greases of claim 6 for the lubrication in applications having temperature ranges between −100 and +180° C. wherein the oil (B2) is that of the class (8). 